Tanning process and tanning agents therefor



United States Patent This invention relates to a process for tanning animal skins and furs, and more particularly to a tanning process wherein resinous condensation products are employed as tanning agents.

We have found that excellent tanning effects can be achieved with the aid of resinous tanning agents, if skins or furs are subjected to a combined tanning process with cationic and anionicresins as the tanning agents. For example, the improvedrtanning efiects can be achieved by first pre-treating the skins'or furs with cationic resins and subsequently treating them with anionic resins, or by reversing the order, i.e. by pro-treating skins or furs withanionic resins and subsequently with cationic resins. The

improved tanning effects produced by the tanning procedure according to the present invention are manifested by an exce lent binding, effect in the skin as well as in the leather, and by improved plumpness, soft feel and improved appearance of the grain ofthe dressed leather. In

this mannerit is possible to achieve tanning effects with resinous tanning agents alone which could heretofore not be achieved in the same manner even by subjecting resintanned skins and furs to an after-treatment with mineral, vegetable or synthetic tanning agents, or with fatty tanning agents.

The softness and elasticity of the deposited resins, and therefore the suppleness of the dressed leather, can be further varied by treating the skins or furs with cation ice forming groups and condensed in the presence of these compounds. Examples of such compounds are alkali metal'sulfites and bisulfites; amino-carboxylic acids, such as aminoacetic acid; aminoalkyl-sulfonic acids, such as taurine; aminoaryLsulfonic acids, such as sulfanilic acid; oxy-carboxylic acids, such as oxalic acid; oxy-sulfonic acids, such as isaethionic acid; formaldehyde-sulfoxylic acid and the like; and salts of the foregoing compounds.

Another method of producing anionic resins comprises condensing dicyanodiamide and formaldehyde in the pres ence of salts of sulfurous acid, as disclosed in copending appl cation Ser. No. 379,478, filed September 10, 1953. This application discloses a process of producing anionic resinous tanning agents by condensing dicyanodiamide, formaldehyde and a salt of sulfurous acid by heating to temperatures above 50 C. in a neutral or slightly alkaline solution. About'l mol of dicyanodiamide to 3.5 to 7 mols of formaldehyde to 0.2 to 0.8 mol' of sulfite salt are employed in the condensation reaction.

In addition to these particular anionic resins, other known natural or synthetic anionic resins may advantageously be used in the process according-to the present invention, for example natural resin acids and the like.

.The salts of the above anionic resins may be formed fromany suitable salt-forming base, particularly from i alkalimetal hydroxides, ammonia or organic bases, such active fatty substances subsequent to or simultaneously with the pretreatment with the cationic resins, and there after treating the skins or furs with anionic resins. Thev same applies to the above-described tanning procedure wherein the sequence is reversed; in that case, however, the pre-treatment with anionic resins must be combined withor followed by a treatment with anion-active fatty substances.

Cation-active and anion-active fatty substances which are suitabe for this purpose are any of the surface-active fatty compounds; such as, for example, quaternary ammonium salts and other onium salts, alkylsulfates, alkylsulfonates, alkylarylsulfonates, sulfonated or sulfited animal and vegetable oils or fats, "and the like.

Within the scope of the present invention, the term anionic resins is intended to designate those resins which contain one or more acid, salt-forming groups in the molecule which have a Water-solubilizing effect upon the entire resin molecule as such orlin the form of its salt. Resins of this type are well known and may be produced in various ways. For example, one method comprises subjecting condensation products of condensableorganic nitrogen compounds, containing aminoor imino-groups, and oxo-compounds to a condensation reaction with compounds containing acid water-solubilizing radicals. Suitabe organic nitrogen compounds which will readily condense with oxo-compounds are, for example, urea, thiourea, methylene-diurea, cyanamide, guanidine, alkylguanidines, dicyanodiamide, dicyanodiamidine, melamine, and the like. Examples of suitable oxo-compounds are formaldehyde, acetaldehyde, compounds yielding such aldehydes, acrolein, furfural, methylethyl ketone, and the like. In order to obtain anionic resins, the above startingmaterials are admixed with compounds containing acid, salt,-

as alcohols, amines and the like.

The term cationic resins, as used herein, is intended to designate those resins which contain one or more basic groups in the molecule which have a Water-solubilizing etfect upon the entire resin molecule as such or in the form of its salt. Resins of this type are also well known, and they are produced from the same condensable organic nitrogen compounds and the same oXo-compounds as those used in the production of the above anionic resins. The resinous condensation products resulting therefrom have, in most cases, inherent cationic characteristics, and may be transformed into water-soluble salts with the aid of suitable inorganic or organic acids. However, there may be imparted additional cationic character by condensing them with further basic components, such as ammonium salts; polyamino compounds, for example polyalkylene-polyamines, such as triethylenetetramine or tetraethylenepentamine; or oxy-alkylamines, such as dimethylamine-ethanol, diethanolamine, oxazolidine, polyphenylb guanidines, and the like.

- Examples of particular cationic resins which may advantageously be employed as tanning agents in the process according to the present invention are theresinous condensation products of urea, dicyanodiamide for melamine with oxocompounds, such as formaldehyde, and watersoluble salts of such resinous condensation products formed by their reaction with inorganic or organic acids. In addition to these specific resins, other known cationic resins or their salts may, however, also be used.

The above mentioned anionic and cationic resins may he used as tanning agents in the present process in the form of preliminary condensates or in the form of final condensates, provided the latter are water-soluble, primarily depending upon thetanning method used and upon the tanning elfect which it is desired to produce. They may form salt-like electroneutral resins in the skins or furs by reacting with each other. If the resins are in a state of preliminary condensation they may be transformed in the skins or furs into a state of final condensation with the aid of acids, salts or by heat.

Instead of applying the anionic and cationic resins in a step-wise manner-4e, by first treating the skins or furs with the anionic resins and subsequently with the cationic resins, or vice versa-the two ionogenic resins may be applied simultaneously. This may be accomplished by impregnating the skins or furs with aqueous solutions of salt-like electroneutral resins, formed by the above anionic resins and cationic resins in the presence of each other.

The tanning process in accordance with the present invention leads to excellent tanning effects, even if no other tanning agent than a resinoustanning agent is used. The process may, however, also be carried out in combination with mineral, synthetic or vegetable tanning agents, or with fatty tanning agents. In that case the skins or furs may be subjected to a preliminary or subsequent treatment with these non-resinous tanning agents, for example in order to impart additional plumpness to the leather. For this purpose the present process is particularly well adapted for use in conjunction with a chromium tanning procedure. if chromium-tanned leather is treated with the resinous tanning agents according to the present invention, the resulting leather is more plump and fine-grained than if the leather is tanned with anionic and cationic resinous tanning agents alone. This is true even if the resinous tanning procedure is combined with a procedure employing vegetable or synthetic tanning agents, whereby, in most cases, coarse-grained leather is produced. As a rule, the best results are obtained with the aid of the process according to the present invention if the skins and furs are first treated with the cationic tanning agent and subsequently with the anionic tanning agent. The amounts of these ionogenic tanning agents which are required to produce the desired results range from 0.5 to 20%, preferably 5 to 7%, for the cationic resinous tauning agents, and from 0.5 to 5%, preferably 1 to 2%, for the anionic resinous tanning agents. It small amounts of the resinous tanning agents are used, for example from 1 to 2% of the cationic resin and 0.5 to 1% of the anionic resin, the skins and furs may be subjected to a chromium tanning treatment with about 1 to 1.5% cr o, in the usual manner. All of the given percentages are based upon the weight of skins or the shaved weight-of the furs.

The present process is thus particularly well adapted for the production of highly plumped chromium leather, whereby the trimmings, i.e. the belly portions and flank portions, are particularly well plumped.

Our process can be used to good advantage for the production of all types of leathers; thatis, for the production of all grades of leather from splits or whole animal skins, such as, for example, from buck and doe skins, lamb skins, sheep skins, kids, goat skins, calf skins, pig skins, cow hides, and other animal skins. Moreover, the process is well adapted for tanning fur skins of all types, such as foal skins, lamb pelts, rabbit pelts, and precious furs, and for tanning reptile skins. With the aid of the process according to the present invention, therefore, it is possible to produce leather of varying characteristics, for example glove leather, apparel leather, shoe-upper leather, suede, leather for industrial purposes and the like.

The following examples will further illustrate our invention and enable others skilled in the art to understand our invention more completely. It is understood, how ever, that the invention is notlimited to the particular quantities, conditions and materials recited in the examples below.

PRODUCTION OF WHITE, SOFT, LIGHT-FAST LEATHER FOR APPAREL (GLOVE LEATHER) Example I Bated sheep and goat skins (pH 7 to 7.5) were immersed into a solution containing 50% water (20 C.) and 4% of a cationic resinous tanning agent produced by subjecting a mixture of 0.5 mol guanidine hydrochloride, 0.5 mol dicyanodiamide and 3.0 mols formaldehyde to a condensation reaction. The skins were allowed to remain in the solution for three hours. Thereafter, approximately 1% of an anionic resinous tanning agent, produced by condensing a mixture of 1 mol dicyanodiamide, 3.5 mols 4 formaldehyde and 0.5 mol sodium bisulfite (diluted wit water to a ratiobetween 1:10 and 1:15), was added in aqueous solution to the cationic tanning bath over a period of from 45 minutes to onehour. The skins were allowed to remain in this solution for an additional hour. At the end of this period, the tanned skins were removed from the bath and allowed to dry on a trestle for a day or two. Thereafter, they were rinsed and fat-liquored with 2 to 4% of a light-fast fat-liquoring oil. The resultand - leather with formic acid to a pH of 4.2 to 4.4 after the 'ous sulfuric acid solution.

treatment with the anionic tanning agent,but while still immersed in the resinous tanning bath, then adding 0.5% Cr O (commercial chromium tanning agent) to the acid bath, allowing the skins to remain therein for 30 minutes to one hour, and then drying, rinsing and fat-liquoring them as above indicated.

Example 11 I period of from 45 minutes to one hour. Subsequently,

the tanned skins were dried, rinsed and fat-liquored as described in the preceding example to achieve the desired softness, plumpness and suppleness.

PRODUCTION OF WHITE UPPER LEATHER Example III Bated calf and cow hides (pH 7 to 7.5) were pickled in a solution containing 100% water, 6% sodium chloride, 1% potassium alumand 0.6 to 0.8% of a 96% aque- Thereafter, 0.5 to 0.8% Cr O (commercial 33% alkaline chromium tanning agent). was added to'the pickling bath, and the skins were allowed to remain therein for about 4 hours without neutralization. The pickled and chromium-tanned skins were thentransferred to a separate tanning bath comprising 50% water (20 C.) and about 5% of an anionic resinous tanning agent produced by condensing 1 mol dicyanodiamide, 3.5 mols formaldehyde and 0.45 mol sodium bisulfite. The skins were allowed to remain in the bath for about two hours, At the end of this period,

an aqueous solution-of l to 2.5% of a cationic resinous tanning agent produced by condensing 1 mol dicyanodiamide and 4.5 mols formaldehyde was added gradually to the bath over a period of about one hour, and the skins were allowed to remain in this solution for an additional hour. Subsequently, the tanned hides were removed from the bath, dried on a trestle for one to two days, rinsed, and-finished with a customary light-fast fatliquoring agent.

PRODUCTION OF HIGHLY PLUMP LEATHER spasms ride, 0.5 mol dicyanodiamide and 3.0 mols formaldehyde was slowly added to the anionic bath over a period of 30 to 45 minutes, and subsequently 0.2 to 0.5% ammonia was added. The bath turned completely clear. The hides were then removed from the bath, neutralized, rinsed, dyed an fat-liquored and finished in the customary manner. A fine-grained leather is obtained which has a pleasant hand and is highly plump, particularly in the softer portions of the skins.

Example V Unneutralized chromium-tanned calf and cow hides (pl-I 3.8 to 4.0) were pared and then immersed into a solution comprising 50% water and 5% of an anionic resinous tanning agent produced by condensing 1 mol dicyanodiamide, 3.5 mols formaldehyde and 0.475 mol sodium bisulfite. The skins were allowed to remain in this bath for 15 to 30 minutes. Thereafter, 0.8 to 1.5%

of a customary leather dye (based on the shaved weight) were added to the anionic bath, and the skins were allowed to remain therein for about 1 /2 hours. end of this time, 1 to 2.5% of a cationic resinous tanning agent produced by condensing 0.5 mol guanidine hydrochloride, 0.5 mol dicyanodiamide and 3.0 mols formaldehyde were gradually added to the anionic bath over a period of about one hour, and the skins were allowed to remain in the bath for an additional half hour. The bath was then neutralized with 0.2 to 0.5% ammonia (in 25% aqueous solution), and after about half an hour the skins were removed and rinsed. The pH of the leather was 5.5. Thereafter, it was fat-liquored, dried and finished in the customary manner. The finished leather was highly plump and had a pleasant hand.

While we have given certain specific embodiments of our invention, We wish it to be understood that various changes and modifications may be made therein without departing from the spirit of the invention or the scope of the appended claims.

We claim:

1. The method of tanning animal skins which comprises applying to said skins two aqueous solutions, by first immersing the untanned skins in one solution containing one resin selected from the group consisting of (1) a 0.5% to 20% aqueous solution of a water-soluble cationic resinous condensation product selected from the group consisting of (a) the water-soluble basic condensation product of about 3 to 4.5 mols of formaldehyde and about 1 mol of a compound selected from the group consisting of dicyanodiamide, melamine and mixtures of dicyanodiamide and guanidine and (b) the water-soluble acid salts of said basic condensation product and (2) a 0.5% to 5% aqueous solution of a water-soluble anionic resinous condensation product of about 3.5 to 7 mols of formaldehyde, about 1 mol of dicyanodiamide and about 0.2 to 0.8 mol of an acid salt-forming compound selected from the group consisting of alkali metal sulfites and alkali metal bisulfites for a time suflicient to substantially At the exhaust the bath and adding thereafter to said bath a sufficient amount of the other of the above resins to give the stated concentration, allowing the skins to remain immersed in said baths for a time sufficient to effect tanning.

2. The method of claim 1 wherein the animal skins are first immersed into an aqueous solution of the cationic resinous condensation product for a time suiiicient to substantially exhaust the bath and the anionic resinous condensation product is then added thereto.

3. The method of claim 1 wherein the animal skins are first immersed into an aqueous solution of the anionic resinous condensation product for a time suflicient to substantially exhaust the bath and the cationic resinous condensation product is then added thereto.

4. The method of claim 1 wherein a compatible fatliquoring agent is added to one of said aqueous solutions containing said animal skins.

5. Tanned skins produced by the method of claim 1.

6. The method of tanning animal skins which comprises immersing said untanned skins into an aqueous solution at about 20 C. containing 5% to 7% of a watersoluble cationic resinous condensation product selected from the group consisting of (a) the water-soluble basic condensation product of 1 mol of an amide selected from the group consisting of dicyanodiamide and mixtures of dicyanodiamide and guanidine wherein 0.5 mol of said mixture is guanidine, and 3.0 to 4.5 mols of formaldehyde and (b) the water-soluble acid salts of said basic condensation product for a time sufiicient to substantially exhaust the bath and adding thereafter to said bath 1% to 2% of a water-soluble anionic resin condensation product of about 1 mol of dicyanodiamide, 0.45 to 0.5 mols of sodium bisulfite and about 3.5 mols of formaldehyde and allowing the skins to remain immersed in the bath for a time suiiicient to effect tanning.

7. The methodof claim 6 wherein a cationic fat-liquoring agent is added to the exhausted solution prior to the addition of said water-soluble anionic resin condensation product.

References Cited in the file of this patent UNITED STATES PATENTS 1,780,636 Stine Nov. 4, 1930 2,092,622 Koch et a1 Sept. 7, 1937 2,205,355 Grimm et a1. June 18, 1940 2,423,185 Gundel et a1 July 1, 1947 2,567,238 Sellet et a1. Sept. 11, 1951 2,637,622 Dawson et al May 5, 1953 2,809,088 Meister Oct. 8, 1957 2,836,480 Honold May 27, 1958 2,847,396 Sellet Aug. 12, 1958 OTHER REFERENCES Schildknecht, Calvin E., Polymer Processes, High Polymers, 1956, vol. X, pp. 340-344. 

1. THE METHOD OF TANNING ANIMAL SKINS WHICH COMPRISES APPLYING TO SAID SKINS TWO AQUEOUS SOLUTIONS, BY FIRST IMMERSING THE UNTANNED SKINS IN ONE SOLUTION CONTAINING ONE RESIN SELECTED FROM THE GROUP CONSISTING OF (1) A 0.5% TO 20% AQUEOUS SOLUTION OF A WATER-SOLUBLE CATIONIC RESINOUS CONDENSATION PRODUCT SELECTED FROM THE GROUP CONSISTING OF (A) THE WATER-SOLUBLE BASIC CONDENSATION PRODUCT OF ABOUT 3 TO 4.5 MOLS OF FORMALDEHYDE AND ABOUT 1 MOL OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF DICYANODIAMIDE, MELAMINE AND MIXTURES OF DICYANODIAMIDE AND GUANIDINE AND (B) THE WATER-SOLUBLE ACID SALTS OF SAID BASIC CONDENSATION PRODUCT AND (2) A 0.5% TO 5% AQUEOUS SOLUTION OF A WATER-SOLUBLE ANIONIC RESINOUS CONDENSATION PRODUCT OF ABOUT 3.5 TO 7 MOLS OF FORMALDEHYDE, ABOUT 1 MOL OF DICYANODIAMIDE AND ABOUT 0.2 TO 0.8 MOL OF AN ACID SALT-FORMING COMPOUND SELECTED FROM THE GROUP CONSISTING OF ALKALI METAL SULFITES AND ALKALI METAL BISULFITES FOR A TIME SUFFICIENT TO SUBSTANTIALLY EXHAUST THE BATH AND ADDING THEREAFTER TO SAID BATH A SUFFICIENT AMOUNT OF THE OTHER OF THE ABOVE RESINS TO GIVE THE STATED CONCENTRATION, ALLOWING THE SKINS TO REMAIN IMMERSED IN SAID BATHS FOR A TIME SUFFICIENT TO EFFECT TANNING. 